1. Field of the Invention
The field of this invention lies within the art of joining plastic pipes or metal to plastic pipes without the aid of an adhesive. More particularly, it involves the utilization of a swaging process and apparatus for joining a plastic pipe into a fitting and accommodating the fitting to a second fitting joined to a second plastic or metal pipe.
2. The Prior Art
The prior art related to the joining of plastic pipes, reinforced plastic pipes, and other non-metallic pipes, oftentimes involves the utilization of a preformed threaded fitting, a frictional fitting, or an adhesive for bonding the pipes together. In other words, the jointure of plastic pipes has been accommodated by pre-established pipe lengths that are threaded or molded with a particular fitting, or if they must be joined in the field, they have been adhesively bonded.
In most cases, it is common to adhesively bond plastic pipes together. One of the major drawbacks of providing pipes with adhesive joints or frictionally fitted joints, is that the plastic pipes cannot take the type of pressures that are generally involved in high pressure applications. In particular, the pipe joint oftentimes is the weakest point of the entire fluid mechanical system. As a consequence, the limitations on the amount of pressure that can be applied in plastic pipe systems is commensurate with the amount of pressure which adhesive bonded pipes can accommodate.
It has been customary in the past to sometimes use threaded pipe fittings for plastic pipes, as well as other types of clamps to join pipes in a fluid mechanical system. However, the utilization of such apparatus has not effectively created a pipe joint which can withstand high pressure and be applied in a field application. The inventor of this invention has established the fact that with certain plastic swaging and locking techniques, plastic pipe can be used in the same manner as metal pipe, or joined to a metal pipe for complete adaptation of plastic pipe in the field with serviceability at certain required pressures.
A further drawback of the prior art is that certain metal and plastic pipe joints were not capable of being spliced. The metal joints would work against the plastic joints and would cause the plastic threads or other joining means to deteriorate over an extended period of time. This invention overcomes such deficiencies by incorporating a fitting which will not deteriorate with time.
In addition to the foregoing advantages, the fittings and devices described hereinafter incorporate the ability to provide for axial as well as lateral displacement of the pipes that have been joined together. In other words, it is oftentimes a requirement in the field that pipes be able to expand and contract in their axial relationship at the joints, as well as being able to laterally move with respect to each other without undue displacement of the joint. When a normal plastic pipe connection has been made, and axial or longitudinal displacement is encountered, the joint has a tendency to deteriorate or fatigue due to such flexure. This invention allows for axial movement within a collar joint, while at the same time providing for an appropriate seal of the pipes. In addition thereto, the invention allows for lateral displacement of the pipes at the joints so that the bending moment of the pipes in their joined relationship can be accommodated with an overriding collar that secures both pipes together.
The process of this invention incorporates a novel means for expanding and swaging a plastic pipe by causing it to cold flow into a surrounding fixture. The surrounding fixture is secured by a metal retainer ring which provides a certain degree of hoop strength. An expandable metallic inner sleeve secured within the pipe is expanded against the outer hoop strength for accommodation of the cold flowing of the plastic and retention thereof. This is accomplished by a hardened elastomer which circumferentially expands the inner sleeve to the point where it is secured tightly against the pipe and holds it against the hoop strength of the outer ring. The end result is to provide for a plastic cold flow type of joint which has been swaged into a fixture.
The fixture is capable of accommodating a mating fixture, or a threaded member. The entire process is one wherein the ability to cold flow and retain plastic in its cold state is provided for by the expansion of the interior metal sleeve against the outer retaining ring. As a consequence, the device is new with respect to the prior art as to its process and the apparatus attendant therewith for the practice of the process.
The adapter or fixture of the invention can also be used to couple threaded steel pipe by being swaged onto the ends of such pipe and held together by means of a holding collar. The adapter is held onto the pipe by yielding of the plastic serrated tooth members against the metal pipe to seal it against the pipe. Thus, the adapter allows for recoupling of plastic and fiberglass reinforced plastic pipes with similar pipes or with metal pipes. The coupling of such pipes allows for the radial as well as axial movement of the pipes when coupled with a holding collar.